Field of the Invention
The invention relates to semi-conductor pressure transducers; and, more particularly, to a silicon transducer having a central integral push rod adapted to transmit pressure applied to the base of the rod to strain gages on the transducer.
It is well known in the art to make pressure transducers having a diaphragm and strain gages embedded therein. Pressure is applied to one side of the diaphragm and the pressure is measured, via the strain gages, on the othe side of the diaphragm. Silicon is a well-known material used in such diaphragms These electrical pressure transducers are used on hospital patients to monitor body functions, such as blood pressure. Dury heat surgery, it is often necessary to use defibulation apparatus, such as pads or electrodes, and these devices involve the use of high voltages. Prior art transducers which have been used in the past to monitor such function usually are blown or damaged or destroyed by the use of such high voltage defibulation apparatus. Further, the patient may be injured when the monitor transducer supplies a direct return to ground for the current.
Also, there are many industrial applications where such transducers are exposed to harsh and corrosive atmospheres. If the diffused sensors of such transducers are exposed to such a harsh environment, they will soon be degraded and rendered useless. There is a need for a transducer that is electrically isolated from the application area thereby keeping the sensors therein shielded from corrosive atmospheres thereby preserving the integrity of such transducers.
As was heretofore mentioned, various prior art transducers are known. In U.S. Pat. No. 4,188,258 to Mounteer et al, a transducer is disclosed having a metal strain gage material formed in a flexible silicon diaphragm. A plurality of spaced mesas are etched into the depth of the diaphragm. These mesas result in a greater strain and bending of the diaphragm in the thinner portions thereof and less strain where the mesas are left intact thereby making the diaphragm prone to blowing in high voltage applications.
In U.S. Pat. No. 4,327,350 to Ericksen, a method of making a pressure transducer is disclosed. Although he does discuss a diaphragm driving a post, the post is not integral and must be bonded at both ends resulting in weakened areas.
In U.S. Pat. No. 4,051,451, a transducer is disclosed having a non-integral push rod. The rod is a loose fitting rod capable of independent up and down movement. It is not bonded but held in place by glass guides and spring means. The rod is used to activate a diffused beam as the sensor. Again, such an arrangement is prone to blowing in high voltage operations.
It can be seen that no prior art electrical pressure transducer includes a single integral push rod. Thus, stress is induced in the sensing elements of such prior art devices.
There is thus a need for an electrical pressure transducer having a silicon diaphragm with a single integral push rod, the silicon diaphragm being electrically isolated from the application area thus making the sensor diaphragm a slave of the isolating diaphragm.